The present invention concerns generally trolling plates used to reduce boat propeller efficiency and hence boat speed to one suitable for trolling.
By way of background, the concept of positioning a baffle or plate structure rearward of a boat propeller for the above noted purpose is well known. To permit increased boat speeds such plates were swingably mounted on a support bracket in place on the lower housing of an outdrive or of an outboard motor with the plate being displaceable out of the propeller wash either manually or by a control from the boat operator's station.
Known trolling plates utilize various lock mechanisms which are subjected, in some instances, to substantial forces as for example when a trolling plate is left inadvertently in the down position when a boat motor is throttled up. Frequently the mechanical failure of a trolling plate renders it unuseable until repaired resulting in lost fishing time and expense to the boat owner.
Another drawback to known trolling plates is the loss of maneuverability. Blocking of a water flow to a propeller rotating in a reverse direction prevents rearward movement of a boat as well as rearward directional changes of the boat.
Prior art pertaining to trolling plates includes U.S. Pat. Nos. 2,719,503; 2,654,336; 1,576,237; 2,256,898; 2,050,336; 3,209,716; 3,965,838 and 4,048,940 to mention a few.
U.S. Pat. No. 5,005,507 issued to the present inventor discloses the novel combination of a hydrofoil and trolling plate unit for attachment to the cavitation plate of an outdrive or lower housing of an outboard motor. U.S. Pat. No. 4,487,152 discloses a hydrofoil in place on a cavitation plate. U.S. Pat. No. 5,127,353 shows a trolling plate on a hydrofoil with the plate locked in a vertical or horizontal position by a pin. A modified form of lock utilizes a bar engageable with slots in the trolling plate.